An error with your Firefox is that it clearly cannot download any file you intended to download. The download manager refuses to popup or show any sign a file is being added at every click of the download button on the webpage you wish to download the file.
An attempt to reinstall Firefox returns with the same problem. It refuses to go away. You have tried everything possible available on online to solve the trouble only to no avail.
This issue is not a bug and it is not a problem coming from Firefox nor is it coming from your Windows operating system.
If you are experiencing this problem with your Firefox while trying to download a file from the internet this information will help you to solve the problem quickly.
Image showing a trusted site to download Malwarebytes
STEP 1: Download Malware removal tool from online or from Malwarebytes trusted LINK by using another computer and copy it to your system.
Image showing Malwarebytes installer
Image showing updating Malwarebytes
STEP 3: Click on Malwarebytes on desktop and allow it to carry out online update.
Image showing Scan tab
STEP 4: Click on Scan to scan your system for Malware and viruses.
Image showing detected Malware and viruses
STEP 5: After scanning delete all return Malware and viruses by completely removing them from your system. It may require a system restart to complete the process.
Image showing a working Firefox Download Manager
STEP 6: After restarting your system, open your Firefox and download the file you intended downloading.